New Integrated Control Technique for Two-Stage Server Power to Improve Efficiency Under the Light-Load Condition

A new control technique for two-stage server power is proposed in this paper. The proposed technique will significantly reduce power consumption under the light-load condition. The basic idea of the proposed control technique is to control both the dc-link voltage of the power factor corrector (PFC) stage and the switching method of the full-bridge stage. Under the light-load condition, the output voltage of the PFC stage is no more fixed and is dynamically adjusted to significantly reduce the switching losses. Moreover, under the light-load condition, the full-bridge stage is with pulsewidth-modulation (PWM) and burst-mode control to reduce the circulating current losses. The former approach will reduce the switching losses due to the reduction of voltage across the power devices. The latter approach will dramatically reduce the circulating current losses caused by the phase-shift control method since phase-shift switching control is replaced by PWM switching control. Moreover, due to the reduction of the dc-link voltage, the switching losses for PWM and burstmode control can be further reduced, as compared to those for fixed dc-link voltage. Experimental results of 480-W server power are presented. It is shown that the efficiency of the two-stage power converter can be improved up to 8% and 3.9% under light-load and 10% load conditions for input voltage = 110 V, respectively. For the 220-V input voltage, the efficiency improvement using the proposed method is 6.4% and 4.2% under light-load and 10% load conditions, respectively.